1. Field of the Invention
This invention relates to a heat roller fixing device for a recording device such as a copier or a printer, especially to a heat roller fixing device having a divided structure which comprises an upper part forming a fixing roller side and a lower part forming a pressing side.
2. Description of the Related Art
As shown in FIG. 12, a heat roller fixing device generally has a fixing roller 2 with a built-in heater 1 and a pressing roller 4 which is mounted via a pressing lever so as to press the fixing roller 2.
A paper sheet 6 with a non-fixed toner image 5 is transported from a transferring part (not shown) and is passed through the nip between the fixing roller 2 and the pressing roller 4 while inlet guides 7a, 7b guide the paper sheet 6. Thereby, the non-fixed toner image is melted and fixed on the paper sheet 6. The paper sheet 6 with the fixed toner image thereon is separated from the fixing roller 2 by a separating pick 8, which is arranged so that the top of the separating pick 8 is in contact with the peripheral surface of the fixing roller 2. Further, the paper sheet 6 with the fixed toner image thereon is discharged to a discharging tray (not shown) by a pair of paper discharging rollers 10, while being guided by sheet discharging guides 9a and 9b.
In such heat roller fixing devices, one end of each of the fixing roller 2 and the pressing roller 4 is provided on a front side plate which is mounted to the front plate of the main body of the recording device, and the other end of each of the fixing roller 2 and the pressing roller 4 is provided on a back side plate which is provided at a driving side having a fixing roller driving element.
When the pair of rollers are assembled, one of the ends of these rollers are first inserted into holes of the back side plate. Next, the other ends of the rollers must be set into the front side plate after these rollers are slid along their lengths. As a result, it is not easy to set and operate the fixing device.
Recently, by making a frame of the fixing device using plastic, the costs have been decreased. Further, a divided structure which comprises an upper part (a fixing roller frame) forming a fixing roller side and a lower part (a pressing roller frame) forming a pressing side, has been put into practice to make it easy to assemble the fixing device.
As shown in FIG. 13 (a), the upper part of the divided structure for the fixing roller is mainly made of a fixing frame 11 having a recess rotatably holding the fixing roller 2, the recess being formed on the fixing frame 11. (As the fixing frame 11 is set after turning it over, the fixing roller 2 is initially supported so as not to drop.)
The divided structure of the pressing roller side (FIG. 13 (b)) also is mainly made of a pressing frame 12 for rotatably holding the pressing roller 4 by a recess which is formed in the pressing frame 12.
The frames 11 and 12 are integrated by screws, etc., to form a fixing device. It is easy to set each of these rollers 2 and 4 into its respective frame 11 or 12 via the recesses in the frames.
However, it is difficult in these fixing devices to correctly position the fixing roller 2 and/or the pressing roller 4 relative to the main body, or to make the rollers 2 and 4 precisely parallel. As a result, troubles (such as wrinkles on a paper sheet, a paper jam in the fixing device and jitters) occur if the positioning of the units is not accurate.
Further, it is difficult to assemble the fixing device if harnesses for connecting the heater to a connector from the main body are provided in the pressing roller unit. That is, after the pressing roller unit and the fixing roller unit are made separately and are integrated, the harnesses must be wired between the fixing roller unit and the pressing roller unit. Furthermore, it is difficult to automatically assemble these units on lines in the factory, so that the cost increases.